Introduction - lcoem

clashjudiciousElectronics - Devices

Nov 8, 2013 (3 years and 7 months ago)

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computer awareness F03



INPUT DEVICES


Introduction

An input device is a piece of hardware that is used to enter data
into a computer.

There are many different kinds of input devices
-

so many in fact,
that we have had to split this section into two seperate mini
websites. This one is about manual input devices. The second
mini website is about automatic input devices.




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Keyboard



The keyboard is the most common and widely used input device.


It is made up of buttons called 'keys'. The keys are arranged into sections:


alphabet keys


Function or F keys (F1, F2, F3)


Numeric keys (one set above the alphabet keys and a numeric keypad on the right)


Arrow keys


Command keys (insert, delete, home, end, page up/down)


Most keyboards are called 'QWERTY' keyboards. This name comes from the first six letters
on the top row of the alphabet keys.



Using a keyboard for too long can lead to health problems such as repetitive strain injury
(RSI). To try to overcome this, different styles of keyboard have been developed, for
example, the ergonomic keyboard. They are supposed to put your hands into a much more
natural position than a traditional keyboard.



Advantages


Most computers come with a keyboard supplied


People are used to using keyboards to enter data, they need very little training


A skilled typist can enter data very quickly


Specialist keyboards are available e.g. ergonomic, gaming keyboards



Disadvantages


It is easy to make mistakes when typing in data


If you can't touch type, it can be time consuming to enter data


Keyboards are not suitable for creating diagrams


Disabled people often find keyboards difficult to use


Excessive use can lead to R.S.I.



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Mouse


A mouse is also called a 'pointing device' because it enables you to control what
happens on the screen by moving the mouse on your desk and pointing, clicking
and selecting items on the screen.


A mouse usually has two buttons, a right and left one and also a central wheel
which allows you to scroll up and down the page (some mice have three or four
buttons). The left and right button have different functions. Left clicking usually
lets you put your cursor at a certain point on the page or lets you choose a menu
item. Right clicking brings you up a list of relevant menu items from which you can
select a task.


Many of the older styles of mice used a ball which moved against two internal
rollers to record the direction that the mouse was being moved in. Recent versions
of mice use 'optical' or 'wireless' technology to track mouse movement.


Advantages


Idea for use with desktop computers


Usually supplied as part of a new computer system


Most computer users are familiar with them and require little training


Works well in conjunction with a keyboard for data entry


Disadvantages


They need a flat space close to the computer


The rollers in mice that use balls can become clogged with grease and grime and
lose their accuracy until cleaned.


Overuse can lead to RSI


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touchpad


A touchpad is an input device which is usually found on a laptop computer.


Because a laptop is meant to be portable, people aren't always able to attach a traditional
mouse, it might be too much hassle or there might not be enough room to use one. A
touchpad can be used in place of a mouse.


By dragging your finger over the surface of the touchpad, sensors underneath detect the
movement direction and speed. The sensors only react to a fingertip and not a pencil or
other object. There are usually two buttons next to the touchpad which are used to replace
the left and right mouse button.



Advantages


Useful for laptops when using a mouse isn't practical


The pad's position is fixed compared to the keyboard, unlike with a traditional mouse


Very short finger movements are required to move the cursor


Disadvantages


Takes practice and skill to control the position of the cursor using the touchpad


Gloves cannot be worn i.e. in a cleanroom environment


Moist, sweaty or calloused fingers can disrupt the signals picked up by the sensors



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Joystick


Joysticks were originally used by pilots as part of an aeroplane's controls and the technology
was developed to let computer gamers experience a more realistic game environment.


You can move joysticks in many directions and the joystick tells the computer which
direction it has been moved into. They also have one or more buttons whose position when
pushed can be read by the computer.


Joysticks can also be used for controlling machines such as cranes, trucks and powered
wheelchairs.


Advantages


They give a better gaming experience for racing or flying styles of computer games


Disadvantages


Some people find joysticks more difficult to control than a traditional mouse.


Joysticks are not particularly robust and can break easily if too much force is used on
them.


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Scanners


Scanners can be used to convert images or text on paper into a digital format that
can be used by the computer.


A scanner works by shining a beam of light onto the surface of the object that you are
scanning. This light is then reflected back onto a sensor that detects the colour of the light.
This is then used to build up the digital image.


Items that are scanned are usually stored in an image format. However, special software
-

Optical Character Recognition
-

can be used to convert text on the paper into text which can
be edited with a word processor. However, the text doesn't always get converted very well
and you could end up with a lot of mistakes.


There are two types of scanner:


Flatbed scanners


Handheld scanners



The most popular type is the flatbed scanner. This is probably the one that you use at
school. They can scan larger images and are more accurate than handheld scanners.


Handheld scanners are usually only a few inches wide and are held in the hand whilst they
are rolled across the document to be scanned. The images produced are generally not as
large or as high quality as those captured



Advantages


Flatbed scanners are very accurate and can produce reasonably high quality images


Any image which is digitised by the scanner can then be included on electronic documents


Images once digitised can be enhanced with a graphics application


Disadvantages


Images can take up a lot of memory space


Images lose some quality in the scanning and digitising process


The quality of the final image is dependent on the quality of the original image





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touch screen


A touch screen is the only device which works as both an input and an output device. You
view the options available to you on the screen (output) and you then use your finger to
touch the option that you have chosen (input).


Touch screens work particularly well with a menu driven interface. For example, a cashpoint
(ATM) at a bank would first of all ask which service you want. You touch the option
'withdraw cash' on the screen. You are then presented with another choice, 'how much cash
do you want to withdraw?'. Once you have chosen how much, you then get other options
such as 'do you want a receipt?'.


Touch screens are easy to use and are often found in public places such as cashpoints at
banks, ticket collection terminals at theatres or airports, information centres at museums.


Touch screens are not commonly used to input large amounts of data because they are not
very accurate and they would be tiring on the hands to use for long periods of time.



Advantages


Easy to use
-

intuitive, don't need much training


No extra peripherals such as a mouse are needed


Software can alter the screen while it is being used, making it more flexible than a concept
keyboard which has a permanent overlay.


Disadvantages


Not suitable for inputting large amounts of data


Not very accurate
-

selecting detailed objects can be difficult with fingers


Tiring to use for long periods


More expensive than alternatives such as a mouse


Not robust
-

can soon become faulty if misused.






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Graphics tablets


Graphics tablets are often use by graphics designers and illustrators.


Using a graphics tablet, a designer can produce much more accurate drawings on the screen
than they could with a mouse or other pointing device. Drawings created using a graphics
tablet can be accurate to within hundredths of an inch.


a graphics tablet consists of a flat pad (the tablet) on which you draw with a special pen. As
you draw on the pad, the image is created on the screen.



Advantages


It is much more natural to draw diagrams with a pencil type implement (the stylus) rather
than with a mouse


A great level of accuracy can be achieved


Disadvantages


Not really suitable for general selection work such as pointing and clicking on menu items


Graphics tablets are much more expensive than a mouse



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microphone


A microphone can be used to input sound.


The sound is detected by the microphone and an electrical signal is transmitted to the
computer. Special hardware is used to convert this analogue data into digital data so it
can be stored and manipulated.


In the last few years a number of voice recognition systems have been developed. These
packages let the user dictate the text into a computer and then convert the speech to text.


Dictating like this can be much quicker than typing but the software isn't perfect and it
can interpret a word
incorrectly.



Concept Keyboard


A concept keyboard is a flat board that contains a grid of buttons. Each button can be
programmed to do whatever you want.


An overlay sheet with pictures or symbols is placed on the grid so that the user can tell
what pressing on different areas will do.


Concept keyboards are used when fast input is needed and are ideally suited to selecting
from a limited range of choices such as fast food restaurants. Checkout tills such as
McDonalds use symbols to make ordering faster and easier. Primary schools often use
them with young children. The overlay image could be a picture of a farmyard. Pressing
on an animal would cause the computer to make the right animal noise.


Concept keyboards are particularly useful for people who would find using an ordinary
keyboard difficult. It is also very handy in locations where an ordinary keyboard might
be damaged e.g. by spillage or dust.


Advantages


Much faster for making non
-
text selections such as menu choices on the till of a fast
-
food
outlet.


The keyboard is waterproof which can be useful where there is dirt or the risk of splashes


Disadvantages


Poor for text or numeric input
-

although some keyboards do include a numeric keypad
so the operator can enter the amount sold.


Limited to the options shown on the keyboard.









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OUPUT DEVICES

Introduction


This section will introduce you to the most common output devices,
ranging from computer monitors to lights.




computer awareness F03

Monitors


A monitor (or screen) is the most commonly used output device.


They come in many different shapes, sizes and forms. In an exam question, you will need to
be able to choose the best type of monitor and then explain your reasons.





The picture on a monitor is made up of thousands of tiny coloured dots called pixels. The
quality and detail of the picture depends on the number of pixels that the monitor can
display. The higher the number of pixels, the better quality the output.


Larger monitors make working at the computer much easier on the eyes, but the larger the
monitor, the more money it costs! Typical monitor sizes are 19 inches.


The two types of monitor that you need to know about are Cathode Ray Tube monitors
(CRT) and Thin Film Transistor monitors (TFTs).



Cathode Ray Tube


CRT monitors are becoming outdated, although you will probably remember using them at
school not very long ago.


They are large and bulky and have a glass screen which makes them fairly robust and
difficult to damage.


They produce quite a lot of heat so when you have an office with lots of them it could get
quite warm. They are also fairly noisy compared to newer TFT monitors.





Thin Film Transistor



TFT monitors used to be very expensive but now the price has come down they are
beginning to replace all of the old CRT monitors. Not only do they look much nicer they
take up a lot less space. They are quieter than CRT monitors and also create less heat.


On the down side they are easier to damage than CRT screens. A few sharp pokes at the
screen with a pencil can cause lasting damage. Another disadvantage is that unless you have
a very high quality TFT monitor, the colours and contrast are not so good as a CRT monitor
and so the picture can look a bit dull.

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Laser Printer



Laser printers are used in many workplaces because they are quiet, they print a
large number of sheets very quickly and they produce high quality documents.


They print in the same way as photocopiers. Powdered ink, called 'Toner', is fused
onto paper by heat and pressure.


You can purchase a laser printer which prints black and white copies only or you
can pick a colour laser printer. Black and white versions are relatively cheap to
purchase and you only need to buy one toner (which is also expensive). Colour
laser printers are still a little too expensive for most people to purchase for home
use although many offices now have at least one colour laser printer.


Advantages


High quality printouts
-

better than ink
-
jet or dot
-
matrix


Fast printouts
-

faster than ink
-
jet or dot
-
matrix


Prints very quietly
-

quieter than ink
-
jet or dot
-
matrix


Cost per page is low
-

cheaper than ink
-
jet or dot
-
matrix


Disadvantages


Most expensive printer type to buy, especially colour lasers


Toner is more expensive than ink
-
jet cartridges


Expensive to repair
-

lots of complex equipment inside


Fairly bulky
-

larger than ink
-
jet printers


Can't use continuous or multi
-
part stationary to create carbon copies like you can
with a dot
-
matrix printer






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Ink
-
jet printers


Ink
-
jet printers have been popular for a long time because they are relatively cheap to buy and most of
them can combine both black and white and colour printing at the same time.


These printers use cartridges which contain ink. They operate by heating the ink as it flows through the
nozzle. The heating process causes a small droplet of ink to form. This is then released as a single dot
which forms part of a letter or image. This is why the printouts often come out of an ink
-
jet printer still
slightly wet.


Colour ink
-
jet printers are ideal for use at home where only a few documents need to be printed and the
quality of the printout doesn't need to be perfect.



Advantages


Cheap to buy
-

cheaper than a laser printer


More compact than a laser printer


Cartridges cost less to replace than toners


Produce good quality printouts better than a dot
-
matrix but not as good as a laser


Speed
-

faster than a dot
-
matrix but not as fast as a laser


Disadvantages


Noisier than a laser printer (but not as noisy as a dot
-
matrix)


Colour printing can be extremely slow


Cost of printouts per page are more expensive than a laser printer


Cartridges need to be replaced more often than a laser printer


Ink will smudge while it is still wet


Colours can become saturated and often don't look the same as on the screen


If not used for a while, the cartridges can dry out



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Dot
-
matrix printers


These were the first type of printers to be used in homes and schools but they are not used
much nowadays.


They are also called 'impact printers'. The print head contains a grid of pins and different
combinations of pins are pushed out to form different characters. The print head then hits a
carbon ribbon leaving an imprint on the paper. This makes them fairly noisy as you can hear
the pins striking the paper.


Dot
-
matrix printers are ideal when you need carbon copies. This is because the print head hits
the paper with enough force that when carbonised paper is used, the impact makes a copy on
the second sheet.


They are also useful when continuous paper needs to be used for example printing large
quantities of invoices or bills. They can be printed onto paper with perforations and then
separated by tearing once the printing is complete



Advantages


Relatively cheap to buy


Low operating costs


Can print on continuous stationary


Create carbon copies using carbonated paper


Robust and will work perfectly well in harsh or dirty conditions such as garages or factories.


Disadvantages


Print quality is poor and important documents are not suitable to give to managers or
customers


Very slow
-

slowest out of all three printers


Noisy
-

you wouldn't want one of these printing all day in the office


Cannot produce colour copies





computer awareness F03

Plotters


Plotters are a specialist type of printer which is able to draw high quality images on
very large pieces of paper, for example 3 foot wide by 10 foot long.


They are used by engineers, architects and map
-
makers to draw plans of buildings,
diagrams of machines or large scale maps. They can also be used for many other
similar tasks.


A plotter differs from a printer in that it draws images using a pen that can be
lowered, raised and moved across the paper to form continuous lines. The
electronically controlled pen is moved around the paper by computer controlled
motors.


There are plotters now which are 'pen
-
less'. these are used for creating high density
drawings .There are three different types of plotter:


Flatbed plotters

-

These hold the paper still while the pens move


Drum plotters

-

These roll the paper over a cylinder


Pinch
-
roller plotters

-

These are a mixture of the two types above




Advantages


Drawings are of the same quality as if an expert drew them


Larger sizes of paper can be used than most printers can manage


Disadvantages


Plotters are slower than printers because each line is drawn separately


They are often more expensive than printers


They do not produce very high quality text printouts





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speakers


Most computers are fitted with a small internal speaker which can produce beeping sounds to alert
you if you make an error.


Computers can also be fitted with a sound card (or chip) which will enable sound to be output through
external speakers. These usually produce a much higher quality sound than the internal speaker.


Advantages


Everyone in the room can hear the output from the computer.


They can help create an atmosphere or ambiance to accompany a presentation


They help blind people to use the computer because text can be converted into sound


Disadvantages


The output from speakers can disturb others who are trying to work


High quality external speakers can be expensive


Lights such as LEDs (Light Emitting Diodes) can be connected to a computer and respond to
electrical signals which tell them to switch on and off.

Lights


Control devices such as lights, buzzers and motors are used when the computer is controlling a
situation such as traffic lights.


Advantages


They can be used in a computer control simulation and help provide evidence that the
simulation is working correctly


They can provide a warning for users with hearing loss who might not be able to hear the error
beeps produced by the internal speaker.


They come in a large range of different colours


Disadvantages


The bulb may break or wear out and need replacing


There may be a loose connection which means the light doesn't switch on even if the circuit or
control program is correct





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Difference Between Impact Printers And Non
-
impact
Printers



impact printers includes
Daisy
-
wheel, dot
-
matrix, and
line printers



Impact printers include all
printers that work by striking
an ink ribbon




Impact printers are noisy,
inexpensive



Non
-
impact printers include
laser printers and ink
-
jet
printers



Nonimpact printers form
characters and images without
direct physical contact
between the printing
mechanism and the paper.



Nonimpact printers, used
almost everywhere now, are
faster and quieter than impact
printers because they have
fewer moving parts



computer awareness F03



STORAGE DEVICES


Introduction

Unless you want to lose all of the work you have done on your
computer, you need to have a way to store it safely.

There are various types of storage devices, different devices are
suitable for different tasks.




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INTRODUCTION

Data can be stored either in the 'internal memory' or on a 'storage device'.

The amount of data and instructions that can be stored is measured in 'bytes'.

One byte contains 8 bits (short for Binary Digit).

This is the smallest unit of data that can be stored. Each 'bit' is represented as a
binary number, either 1 or 0.

A single keyboard character such as the letter A or T takes one byte of storage.



We normally refer to the capacity of a storage device in terms of Kilobytes (KB),
Megabytes (MB), Gigabytes (GB)
-

or even Terabytes!



Information

Bit Smallest unit of data, either a 0 or 1

Byte 8 bits

Kilobyte (Kb) Assumed to be 1,000 bytes. In reality, it is really 1,024 bytes.

Megabyte (Mb) 1,000 kilobytes (1,024 Kb)

Gigabyte (Gb) 1,000 megabytes (1,024 Mb)





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ROM &
RAM


ROM(read only memory)



ROM is a special kind of memory which stores the instructions which the computer uses
when it 'boots up'
-

the BIOS (basic input output system). It allows it to check the type of
hard disk installed, the amount of RAM installed ,the type of CPU being used etc.


Because the data is 'read only', it can be read but not changed by the user.



The ROM chip (although there may be more than one) is attached to the Motherboard.


The key thing to remember about ROM is that the data is not erased when the computer is
switched off
-

the data is stored permenantly. This type of memory is called 'non volatile
memory'



RAM(random access memory)


How many times have you worked for a whole lesson on something which you were just
about to save but then the computer crashed or your mate 'accidentally' switched it off.
When you rebootrd and logged back in, your work was gone forever.


This was because your work was stored in RAM, or 'temporary memory'. It was fairly safe
there while the computer was working, but as soon as it was switched off, everything
disappeared. This type of memory known as 'volatile memory'.


As well as storing the data you are working on, RAM also stores the modules that are
needed to make your applications work. For example, when you open up Microsoft Word,
you may notice a short delay while the modules are loaded into RAM.


RAM is also needed so that you can have multiple windows open and so that you can
switch between them.


However, if you have a lot of windows, documents and different applications running, you
might find that your system starts to slow down. This is because your RAM is full up and it
is having to decide what it needs to keep stored in memory at any given time and what it
can release. If this happens to you a lot, you can improve the performance of your computer
by installing extra RAM.


Most computers are typically sold with 512Mb
-

1Gb of RAM installed.



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hard disk


The hard disk is the main storage device in your computer. It is a bit like a filing cabinet:
all of your data files and applications software are stored on it.


The hard disk contains a number of metal platters which have been coated with a special
magnetic material. The data is stored in this magnetic material. Thus, the hard disk is
known as a magnetic storage device.


In order to access the data, the platters spin many thousands of times a second and a
magnetic read and write head floats just above the surface of the platter.


When you hear the term 'hard disk crash', this refers to the read/write head crashing down
onto the surface of the hard disk. There is a risk every time this happens that the data
stored in the section just where the head crashes might be damaged. That is why it is a bad
idea just to switch the computer off at the wall without shutting it down properly.


Hard disks are measured in Gigabytes. A typical hard disk size will be around 120 Gb
-

1
Terabyte.


It is possible to also have an external hard disk which can be plugged into the computer
and used to back up your data and then stored in a different place to keep it safe.


Advantages


necessary to support the way your computer works


large storage capacity


stores and retrieves data much faster than a floppy disk or CD/DVD


Stored items are not lost when you switch off the computer


Cheap on a cost per megabyte compared to other storage devices


Disadvantages


Far slower to access data than ROM or RAM chips


Hard disks can crash which stop the computer from working


Regular crashes can damage the surface of the disk, leading to loss of data in that sector


The disk is fixed inside the computer and cannot easily be transferred to another computer.


computer awareness F03

Floppy disks



Floppy disks are one of the oldest types of portable storage devices still in use, having been
around since the 1980s. However, they are gradually becoming obsolete and some
manufacturers are now starting to build their PCs without floppy disk drives.

A floppy disk can store up to 1.44 Mb of data which is equivalent to around 300 pages of A4
text. They used to be the ideal storage device for transferring small files from home to
work/school or from one office computer to another. But nowdays, many files contain
graphics or WordArt and are larger than the size of the floppy disk.

Floppy disks are a magnetic storage device.

All disks must be formatted before data can be written to the disk. Formatting divides the
disk up into sections or sectors onto which data files are stored. In the past, the user would
have to format their own disks, but now they are sold pre
-
formatted.

Advantages


necessary to support the way your computer works


large storage capacity


stores and retrieves data much faster than a floppy disk or CD/DVD


Stored items are not lost when you switch off the computer


Cheap on a cost per megabyte compared to other storage devices


Disadvantages


Far slower to access data than ROM or RAM chips


Hard disks can crash which stop the computer from working


Regular crashes can damage the surface of the disk, leading to loss of data in that sector


The disk is fixed inside the computer and cannot easily be transferred to another computer.

computer awareness F03

Zip disks


Zip disks are pretty much obselete now. However, they were very popular as a backup
medium before CD
-
RWs were developed and became cheap enough for everyone to use.


Zip disks look similar to a floppy disk but are a little bit thicker.


Computers generally didn't come with a zip drive installed, so you couldn't just use one in
the same way as a floppy disk. You needed a seperate plug in drive, which was an extra
expense.


They can store around 100Mb of data
-

70 times more than a floppy disk.



Advantages


Stores more data than a floppy disk


Compresses data, reducing the file size, so more data can be stored


Portable



Disadvantages


Almost obselete now


Need a seperate zip drive to read the disk


More expensive than floppy disks

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Microfilm and microfiche


Microfilm is an analog storage medium for books, periodicals, legal documents
and engineering drawings. Its most standard form is a roll of black and white
35mm photographic film. Another form, more common for engineering
drawings, is a Hollerith punch card that mounts a single exposure. Most
microfilm media have a digital indexing system exposed on the edge of each
image, but these data are not required to use the microfilm, but rather to support
automated retrieval systems. Microfilm is not the most compact analog
microform in wide use. Microfiche is more compact.


Advantages


The medium has numerous advantages:


First, it is compact, with far smaller storage costs than paper documents.
Generally, a year of a periodical in microfilm form takes 10% of the space and
3% of the weight of its paper version.


Second, it is lower cost than a standard subscription. Most microfilm services get
a bulk discount on reproduction rights, and have lower reproduction costs than a
comparable amount of printed paper.


Third, it is a stable archival form. Most library microfilms use polyester with
silver
-
halide dyes in hard gelatin, with an estimated life of 500 years in air
-
conditioning. In tropical climates with high humidity, fungus eats the gelatin used
to hold silver
-
halide. In the tropics, diazo
-
based systems with shorter archival
lives (20 years) are preferable, because they have polyester or epoxy surfaces.


Fourth, since it is analog (an actual image of the original data), it is easy to view.
( much like analog phonograph records having the sound waves carved into the
vinyl) Unlike digital media, the data format is instantly comprehensible to
persons literate in the language; the only additional equipment that is needed is a
simple magnifying glass. This reduces the possibility of incompatibility and
obsolescence.

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Disadvantages



The medium has numerous disadvantages: The principal disadvantage of
microfilm is that the image is too small to read with the naked eye. Special
readers are required to project full
-
size images on a ground
-
glass screen or a flat
reading surface. Hard
-
copy reproduction: A conventional photocopier cannot
reproduce the images and a special combined scanner/printer is required.
Libraries using microfilm often have a very limited number of these viewers that
can produce a photocopy of an image, for a nominal fee. Storage space: Shelf
space is required to maintain an efficient archive as well as a safe and secure
storage environment. Actual reproduction: the microfilm itself can only be
reproduced a limited number of times, while digital media regenerate and often
include error detection and correction schemes.


Uses


Systems that mount microfilm images in punch cards have been widely used for
archival storage of engineering information. For example, when airlines demand
archival engineering drawings to support purchased equipment (in case the
vendor goes out of business), (as of 1999) they normally specified punch
-
card
-
mounted microfilm with an industry
-
standard indexing system punched into the
card. This permits automated reproduction, as well as permitting mechanical
card
-
sorting equipment to sort and select microfilm drawings. Hollerith
-
mounted
microfilm is roughly 3% of the size and space of conventional paper or vellum
engineering drawings. Some military contracts around 1980 began to specify
digital storage of engineering and maintenance data because the expenses were
even lower than microfilm, but these programs are now finding it difficult to
purchase new readers for the old formats. Microfilm first saw military use during
the Franco
-
Prussian War of 1870
-
71. During the Siege of Paris, the only way for
the provincial government in Tours was by pigeon post, and as the pigeons could
not carry paper dispatches, the Tours government turned to microfilm. Using a
microphotography unit evacuated from Paris before the siege, clerks in Tours
photograped paper dispatches and compressed them to microfilm, which were
carried by homing pigeons into Paris and projected by magic lantern while clerks
copied the dispatches onto paper. Each pigeon
-
load of microfilm was capable of
containing up to 40,000 microphotographed dispatches

computer awareness F03


Magnetic Tape



The amount of work that you do on your computer at home can easily be backed
up onto a CD
-
RW or a memory stick. However, many organisations, such as your
school or an office, need to back up large volumes of data each day. A CD
-
RW,
DVD
-
RW or flash memory sticks just would not be large enough for doing this.


Large organisations who need to back up their systems daily tend to use magnetic
tapes to store their data.



Magnetic tape uses 'serial access' to find a piece of data. It works in much the
same way as a video tape that you might have at home. To find a specific piece of
data, you have to start at the beginning of the tape and continue fast forwarding
until you get to the piece of data that you need. This makes it fairly slow to find
and retrieve data so it would not be much use to store data that you needed to get
hold of quickly.



Advantages


relatively cheap per megabyte of storage


can store large amounts of data
-

over 100 Gb


can be set up to do the back up overnight or over the weekend


Disadvantages


serial access so can be quite slow to access data


need a special piece of equipment to record and read the data on the tape








computer awareness F03

CD
-
ROM


Compact Disks come in three main forms:


CD
-
ROM

-

CD Read Only Memory. This means that when you buy the disk, it already has
the data or program stored on it. You can read it, but can't save to it. An example would be a
music CD that you buy from a shop.


CD
-
WORM

-

CD Write Once Read Many. This means that you are able to save to this disk
one time, so you can store your data or an application on it of your choice. However, once
you have saved onto the disk once, you can access the data many times but can't save onto it
again.


CD
-
RW
-

CD Read Write. This means that you can save data to your disk over and over
again, just like you can with a floppy disk.


Compact disks are known as optical storage devices. Data is burned onto the surface of the
disk using a laser beam in the CD drive. A laser beam is also used to read the data stored on
the disk.


A typical CD can store around 650 Mb of data
-

equivalent to 450 floppy disks.



Advantages


Small and portable


Very cheap to produce


Most computers can read CDs. If there is no CD drive, a DVD drive can usually read them


Fairly fast to access the data
-

quicker than a floppy disk or magnetic tape


Disadvantages


Fairly fragile, easy to snap or scratch


Smaller storage capacity than a hard drive or DVD


Slower to access than the hard disk.





computer awareness F03

DVD(digital versatile disk)


DVDs are amongst the most common methods of copying and backing up data at
home.


A DVD is similar to a CD in that it is an optical device and that a laser is used to
store the data and read the data.


A single sided DVD can store about 4.7Gb of data. DVDs which store data on
both sides can hold over 9Gb of data.


One problem with the DVD is that the different companies which make them
haven't agreed on a standard format. Because of this, you will see various kinds of
DVD disks for sale: DVD
-
R, DVD+R, DVD
-
RW and DVD+RW. You have to
make sure that you buy the right kind of disk to go with your DVD equipment.





Advantages


Very large storage capacity


Sound and picture quality is excellent, making them ideal for storing films with
video and sound.


DVDs are now mass produced so they are relatively cheap


DVD players can read CDs


Disadvantages


DVDs do not work in CD drives


There is no single standard of DVD


They can be easily damaged by breaking or scratching



computer awareness F03

Flash memory



Flash memory storage devices are typically small, lightweight, removable and rewritable.
They consist of a small printed circuit board which is encased in plastic or metal casing.
They usually have a removable cap which covers and protects the part of the stick which is
inserted into a USB port.


Memory sticks are available from 1 Gb up to 8 Gb.



Advantages


They are more compact and portable than floppy disks or CDs/DVDs.


They hold more data than a floppy disk and nowadays often more than a CD.


They are more reliable than a floppy disk because they have no moving parts


They are being developed with fashionable looking outer casings and are almost
becoming a 'fashion accessory' much in the way of a mobile phone.



Disadvantages


At the moment, the cost per megabyte of storage is more expensive than floppy disks,
CDs or DVDs.


They can be easily lost


The metal part which is inserted into the USB port can be snapped off if they are
handled roughly


computer awareness F03

operating system

What is an operating system?

An operating system is the program that, after being initially loaded into the computer,

manages all the other programs in a computer.

Functions of an OS

Processor management ,Memory management ,Device management

Storage management, Application interface, User interface


There are two main categories of software. There is 'application software' with examples
such as word processors, spreadsheets and databases. The other main category is called
'system software' which includes the operating system and utility programs.


Once your computer has begun booting up using the BIOS instructions in ROM, the
operating system will be the first piece of software to be loaded up.


The operating system is needed to control everything happening in your computer. It
controls the memory, the disks, the periperals and the application software.


. Examples of operating systems


There are a number of operating systems that you could use on your computer.


The one that you are are most likely to be familiar with is one of the
Microsoft Windows

operating systems.


Almost all personal computers are loaded with Windows before you purchase them and
most schools use a network version.



If you use an Apple Mac computer then you will be familiar with Apple's unique operating
system,
Mac OS
.


Many people find this far easier and more intuitive than Microsoft's Windows versions.





Linux

is an alternative operating system for most computers.


It has the advantage of being free of charge. This is because it is 'open source' software.


Unix



A powerful operating system commonly found on large systems such as super
-
computers
and mainframes. It is especially good at allowing many users to use the computer system at
the same time.






computer awareness F03


Single user operating system


Many of you will have a computer at home and as mentioned on the previous page, it is likely to have
either Microsoft Windows or Mac OS loaded onto it.


Whilst you are using your computer it is likely that you don't need to share periperhals e.g. a printer and
you probably don't need to share out your processing time with another person in the house.


Therefore, the operating system on your computer only has to deal with the tasks you are giving it. It
doesn't need to worry about sharing out memory, hardware or processing time.


This is called a single user operating system.


Examples of such operating systems are Microsoft Windows 95, 98, 2000, XP and Vista as well as the
Mac OS range.



Multi user operating system


Large companies often use a mainframe computer system. These are very expensive, powerful
machines and it would make no sense at all for only one person to be able to use the computer.


However, a mainframe computer can only do one thing at a time
-

even if it does it very quickly. So, to
allow the mainframe to be able to deal with hundreds of people who all want to do something different,
multi
-
user operating systems were developed.


Multi
-
user operating systems work by 'slicing' up the processing time of the CPU into tiny chunks. Each
chunk of time is given to a user to deal with their task. See the diagram below to explain.












TIME SLICES


As you can see, the person on the computer/terminal A gets a little slice of the CPU time before the
person on terminal B. Once his time is up, even if the task isn't completed, person B gets a slice of the
time. However, this happens so quickly, (billionths of a second) that users don't realise that they are
having to share the computer with others

Terminal C

Terminal B

Terminal A

Central processor

A

B

C

A

B

C

B

C

computer awareness F03









Multi tasking operating system


When you are working on the computer you probably have a web browser open, an
email or instant messaging system open and one or more applications such as a
word processor, spreadsheet or graphics package open.


You are able to do this because your operating system will switch the application
modules in and out of RAM as you are using them and return them temporarily to
the hard disk when they are open but not being accessed.


This is called multi tasking.






Real time processing



Real time processing is usually found in systems which use computer control.


This processing method is used when it is essential that the input request is dealt
with quickly enough so as to be able to control an output properly. For example, the
computer inside the Engine Control Unit in a car has to manage the engine at every
moment based on what the driver wants to do.


Real time processing has to be programmed very carefully to ensure that no input
events are missed.


Note that real
-
time processing does not have to be 'fast'. For example, a traffic light
system is a real
-
time system but it only needs to process data relatively slowly. On
the other hand, controlling a car engine has to deal with input events happening
every thousandth of a second so a very fast computer is needed to do this
-
but both
the traffic
-
light and the car engine computers are carrying out 'real
-
time'
processing.


Examples:


Traffic lights


Heart rate monitoring


Aircraft control


Computer games



computer awareness F03



Transaction processing



Inputs are noted by the computer, but it deals with them after a short delay. It spends that
delay handling other inputs and managing data movements.


The delay may be so brief that it looks to you as if it has happened straight away. But in
terms of 'computer time', where each computer cycle is far less than a millionth of a second,
it will have spent many cycles doing other things.



For example,


Booking pop concert tickets


Ordering books online


Handling bank accounts



Batch processing



It is often not desirable to deal with the inputs until a certain number have occurred or a set
time has passed.


So they are stored until the system comes online to process the data in one
'batch'.


Batch processing is usually fully automatic unlike 'real
-
time' or transaction processing which
are interactive.


For example


A stock control programme may store records of every item sold in a shop that day.
Then, at the end of each day it calculates what needs to be ordered.




An online competition stores all the entries until it is time to find the winner.


Electricity, gas and telephone bills are usually calculated on a monthly basis.



computer awareness F03







Central processing system(CPU)


The CPU can be divided into 3 parts.they are control units,arithmatic and logic unit and
main memory.


The central control unit control steps
-
by
-
steps runnning of the computer.it sends the electric
signal to various parts of the system.the ALU does all the calculating and perform the
logical operation.the main operation of the main memory is to stores all the programs and
the data that are being used.as the data or program are needed immediately,the memory is
immediately accessible.The input and output buffer are part of the CPU where data are
stored temporarily to with the difference in speed.with the various peripheral devices.














a

Input

device


Output

device

Backing store

Input
buffer

output
buffer

Main
memory

Control
unit

ALU

computer awareness F03




CONTROL

UNIT



The

control

unit

maintains

order

within

the
computer

system

and

directs

the

flow

of

traffic (operations)
and data. The flow of control is indicated
by

the

dotted

arrows

on

figure

1
-
1.



The

CU selects

one

program

statement

at

a

time

from

the
program

storage

area,

interprets

the

statement,

and
sends

the

appropriate

electronic

impulses

to

the arithmetic
-
logic unit and storage section to cause them to carry out the
instruction.



The

control

unit

does

not

perform

the

actual
processing

operations

on

the

data.

Specifically,

the control unit
manages the operations of the CPU, be it a single
-
chip

microprocessor

or

a

fill
-
size

mainframe. Like a traffic
director, it decides when to start and stop
(control

and

timing),

what

to

do

(program

instructions),
where

to

keep

information

(memory),

and

with

what devices to
communicate (I/O). It controls the flow of all
data

entering

and

leaving

the

computer.

It

accomplishes
this

by

communicating

or

interfacing

with

the arithmetic
-
logic

unit,

memory,

and

I/O

areas.

It provides the computer
with the ability to function under program

control.
Depending

on

the

design

of

the
computer,

the

CPU

can

also

have

the

capability

to
function

under

manual

control

through

man/machine interfacing.

computer awareness F03


The control unit consists of several basic logically defined

areas.
These

logically

defined

areas

work closely with each other.



Timing
in a computer regulates
the

flow

of

signals

that

control

the

operation

of

the computer.


The
instruction and control
portion makes up

the

decision
-
making

and

memory
-
type

functions.
Addressing

is

the

process

of

locating

the

operand
(specific

information)

for

a

given

operation.



An
interrupt

is a break in the normal flow of operation of a
computer

(e.g.,

CTRL

+

ALT

+

DEL).



Control

memory

is

a

random
-
access

memory

(RAM)
consisting

of

addressable

storage

registers.
Cache

memory

is

a

small,

high
-
speed

RAM

buffer

located between
the CPU and main memory; it can increase the speed of the PC.


Read
-
only memory
(ROM) are chips
with

a

set

of

software

instructions

supplied

by

the manufacturer
built into them that enables the computer to perform its I/O
operations. The control unit is also capable of shutting down the
computer

when

the

power

supply

detects

abnormal conditions.


computer awareness F03

ARITHMETIC
-
LOGIC

UNIT


ARITHMETIC
-
LOGIC

UNIT

The

arithmetic
-
logic

unit

(ALU)

performs

all
arithmetic

operations

(addition,

subtraction,
multiplication,

and

division)

and

logic

operations
.Logic

operations

test

various

conditions

encountere
d during processing and allow for different actions to
be taken based on the results. The data required to
perform the arithmetic and logical functions are inputs
from the designated CPU registers and operands.
The

ALU

relies

on

basic

items

to

perform

its
operations.

These

include

number

systems,

data

rou
ting
circuits

(adders/subtracters),

timing,

instructions,
operands,

and

registers.



computer awareness F03

PRIMARY

STORAGE

(MAIN

MEMORY)


PRIMARY

STORAGE

(MAIN

MEMORY)

The

primary

storage

section

(also

called

intern
al

storage, main storage, main memory,

or just
memory)

serves

four

purposes: . To hold data
transferred from an I/O device to the
input
storage area,

where it remains until the computer
is ready to process
it.

To

hold

both

the

data

being

processed

and

the intermediate

results

of

the

arithmetic
-
logic
operations.

This

is

a

working

storage

area

within

the

storage

section.

It

is

sometimes
referred to as a
scratch pad
memory. .



computer awareness F03

Operating Systems

computer awareness F03

Operating Systems


All desktop computers use an
operating system.


Common desktop operating systems
include:



Windows


OS X


Linux



There are hundreds of other operating
systems available for special
-
purpose
applications e.g. mobile phones

computer awareness F03

Functions of an OS


Processor
management


Memory management


Device management


Storage management


Application interface


User interface


computer awareness F03

Processor Management


The OS has manage the execution of
processes so that you believe that there are
several things happening at once.


However,
the processor
can only do one thing at
a time.

In order to give
the appearance of lots of
things happening at the
same time, the OS has to
switch between
different processes

thousands of times a
second making sure that
each process and
application receives
enough of the processor's
time to function properly.

computer awareness F03

Memory Management


The OS
manages memory

(
RAM
). When applications
are loaded they need
memory to work with. The
OS allocates software RAM
to work in. It ensures that
the RAM allocated is not
used by another application.



The OS also manages
virtual memory
. In this
way the computer can run
more applications than it has
RAM for. For example if a
computer was running a
word processor and the user
wanted to load a spreadsheet
application at the same time
and there was not enough
RAM then the OS uses the
hard disc as virtual RAM.

computer awareness F03

Device Management
(Input/Output)


The OS makes use of
queues

and
buffers
,
special storage facilities that take a stream of
bits (data) from a device, e.g. a keyboard, hold
those bits, and then release them to the CPU at a
rate slow enough for the CPU to cope with.



This function is very important when a number
of processes are running and taking up
processor time. The OS will instruct a buffer to
continue taking input from the device, but to
stop sending data to the CPU while the process
using the input is suspended. Then, when the
process needing input is made active once
again, the OS will command the buffer to send
data.

computer awareness F03

Device Management
(Drivers)


The operating system needs to
communicate with the various
hardware
components

which make up the computer.
Special programs called
drivers

enable the
OS to communicate with these hardware
devices. Drivers are needed as the
hardware which makes up a PC may be
vastly different to that of another PC with
the same OS installed.



Drivers are translation programs which
convert the messages from the OS into
messages that the hardware device can
understand.

computer awareness F03

Application Interface


In much the same way that
drivers provide a way for
applications (software) to
make use of hardware
without having to know
every detail of the
hardware's operation,
application program
interfaces

(APIs) let
application programmers use
functions of the computer
and operating system
without having to directly
keep track of all the details
in the CPU's operation.

Think of an API as a
set of
common

routines, protocols,
and tools for
building software
applications. A good
API makes it easier
to develop a
program by
providing all the
building blocks. A
programmer puts
the blocks together.

computer awareness F03

User Interface


The
user interface

(UI) brings structure to the
interaction between a user and the computer.




In desktop computers
the user interface is a
program or set of
programs that sits as
a
layer above the
OS
. The core
operating
-
system
functions
-

the
management of the
computer system
-

lie
in the kernel of the
operating system. The
display manager

is
separate, though it
may be tied tightly to
the
kernel

beneath.

Mac OS X GUI